In general, a strut-type suspension is mainly used in a front wheel of a four-wheeled motor vehicle, and is constructed such that a strut assembly incorporating a hydraulic shock absorber in an outer cylinder formed integrally with a main shaft is combined with a suspension coil spring. Among such suspensions, there is a type of structure in which the axis of the suspension coil spring is actively offset with respect to the axis of the strut, so as to allow the sliding of a piston rod of the shock absorber incorporated in the strut to be effected smoothly. There is another type of structure in which the suspension coil spring is disposed by aligning the axis of the suspension coil spring with the axis of the strut. In either structure, a thrust bearing is disposed between a mounting member for a motor vehicle body and an upper spring seat member of the suspension coil spring to allow the rotation to be effected smoothly when the strut assembly rotates together with the suspension coil spring by the steering operation.
In this thrust bearing, a rolling bearing using balls or needles, or a synthetic resin-made sliding bearing is used. The rolling bearing is extremely favorable since it is capable of lowering the friction torque and effecting the steering operation lightly. However, since the rolling bearing is expensive, in a case where a low price is required, a sliding bearing instead of the rolling bearing is used as the thrust bearing.
Incidentally, either thrust bearing is interposed between the mounting member for the motor vehicle body and the upper spring seat member of the suspension coil spring, as described above. However, since the upper spring seat member is generally made of sheet metal, the upper spring seat member is relatively heavy. In addition, as a result of the fact that the upper spring seat member made of sheet metal needs to be provided with coating for the prevention of rust, even if the sliding bearing is used instead of the expensive rolling bearing to attain the light weight and a low price of the undercarriage of the motor vehicle, there is a limit to such attempts for the light weight and the low price owing to the weight, manufacturing cost, assembly cost, and the like of the upper spring seat member.
The present invention has been devised in view of the above-described aspects, and its object is to provide a strut sliding bearing which makes it possible to omit the upper spring seat member made of sheet metal, thereby making it possible to attain the light weight and a low price of the undercarriage of a motor vehicle.